1. Field of the Invention
The invention relates generally to the field of composite design and more specifically to the field of structural detail fabrication.
2. Description of the Related Art
Laminates contain fibers having a given direction of the fibers within a resin. Unidirectional laminates are usually suitable for carrying loads in only one direction. They are usually weak in the transverse direction to ply orientation. The properties of unidirectional composites are quite different from isotropic materials. Unidirectional materials are highly anisotropic and have exceptional properties, for example, strength, in the fiber direction and mediocre properties perpendicular to the fiber direction. On the other hand, isotropic laminates may be equally strong in all directions.
There are limited applications where composites are used (or bear a load) purely in a unidirectional configuration. In most applications, there will be some loading away from the direction of the fibers. In this situation, if a unidirectional laminate is used, it is only the resin, which is not itself reinforced, that resists this off-axis load. Hence, composite structures are conventionally made by combining unidirectional fibers in different directions relative to one another to enhance load bearing capacity. Such laminates are known as multi-directional laminates.
Stacking laminates with plies in different orientations is useful when there is a need to optimize multi-directional load-carrying capacity. One common way of creating these multi-directional laminates is to layer the laminates with each laminate layer having a ply bias or fiber orientation angle different from the next. A common sequence of layering uses ply bias angles of +45°, −45°, 0° and 90° relative to the reference plane defined by the component to be built. For example, the reference plane may be defined relative to the long axis of a long, straight component such as a stringer, or relative to the central axis of a radial component such as a frame for a fuselage. This sequential stacking of additional ply bias angles creates an isotropic laminate that is more suitable for carrying loads in more than one direction. However, in order to form a circular axis, such as the central axis of a fuselage frame, some material must be sectioned and/or positioned at an orientation that is not ideal, potentially leading to lower strengths, increased labor, manufacturing time and waste.
Orientation requirements for conventional isotropic composite lay ups require layer by layer application of laminates to a bond tool, for example using laminates having the +45, −45, 0 and 90 degree ply angles described above. Thus, conventional methods of manufacturing larger composite parts with curved portions may require the use of multiple ply sections for each ply layer in order to maintain the ply orientation tolerance necessary to create an isotropic composite structure.